Varying exposure during scanning via a 2-pass method

8mm home movies, if the amateur cameraman wasn't careful with his settings, can have the problem of exposure varying widely from scene to scene. And even though varying the frame-to-frame exposure during scanning is undesirable, I can see that there might be benefits in altering the exposure scene-to-scene.

Ques 1

Are any high-end scanners capable of doing a 2-pass scan? i.e. the first 'preview' pass works out where the scene changes are and calculates exposure; then during the second pass, the exposure is altered to boost dark scenes, or reduce bright scenes.

Some providers offer a manual version of the above – a "best light" service whereby they go through the footage scene-by-scene and balance out any inconsistencies in the lighting, whether under or over-exposed.

Quite a lot of homebuilt s8 scanners will do an HDR pass, where each frame is flashed two or even three times (two or three times per colour channel, if it's a monochrome sensor and RGB backlights). This seems to create data which is capable of representing the entire density range of the optical medium, so variations can be worked out in software.

There are two-pass scanners designed to maximize the dynamic range available in the original piece of film, but a film scan is not really designed to fix exposures, they are just supposed to get you everything possible off of the original film for later color-correction.

Thanks for the responses. Not the most sensible idea I've thought of. Came to me when I was thinking of how Premiere improves the quality of its exports by using a 2-pass render. But a 2-pass scan: a bit sus.

However, the mention of each frame being flashed more than once reminded me of something I'd read, and I eventually found it again: the triple-flash of Lasergraphic's Director.

Ques

Does triple-flash mean that you end up with three files from each scan? Much like when you set a digital camera to take three exposures: normal, +1, -1?

The lasergraphics director uses a monochrome sensor with RGB light source so in the HDR mode each frame is flashed either 6x or 9x and it combines the data in the raw output.The Director however is not capable scanning 8mm film, 8mm is only available on the Scan Station which does not have hdr capabilities.

My Nikon film scanner (for stills only:), has a multiscan feature to maximize dynamic range from the scan. From my experience, all color negative film's dynamic range fits within a single pass, and multiscan has no benefit. Multiscan does help sometimes with reversal film (slide film), but it's also limited by the limited dynamic range of the original slide, but it helps pull a little detail out of the most dense areas at the expense of long scanning times.

My Nikon film scanner (for stills only:), has a multiscan feature to maximize dynamic range from the scan.

I assume by "Nikon Film Scanner" that you mean one of the Coolscans. I was not aware they had a multiscan feature. The Coolscan 5000 has a Multipass feature, but that's intended for reducing noise. See the tests done by Martin Ranger (website now gone) which I've archived here: http://www.mediafire...b/Documents.zip

He concludes:

While Multipass Scanning does not seem to degrade the sharpness of the scans, it offers little benefit in the form of reduced analog noise. Given the significant increase in scanning time, one might think twice about using it.